Automatic transmission for hydraulic drive auxiliary speed change gear

ABSTRACT

An automatic transmission for a hydraulic excavator or the like has an auxiliary speed change gear, capable of changing between high and low speeds, and an automatic change-over valve in a hydraulic circuit which connects the high and low speed clutches and a clutch operating hydraulic pump. One end of the automatic change-over valve is connected to the discharge side of the pump by a conduit containing an automatic speed changing valve. A rotation sensing hydraulic source is coupled to a shaft of the auxiliary speed change gear. A hydraulic circuit connects the discharge side of the rotation sensing hydraulic source to one end of the automatic speed changing valve. The automatic speed changing valve changes over the clutches automatically, without damaging the hydraulic motor driving the clutches.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission for a hydraulicallydriven vehicle, and more particularly, to an automatic transmission fora hydraulic excavator or the like which has an auxiliary speed changegear capable of shifting between high and low speed ranges.

2. Description of the Related Art

In a conventional hydraulic excavator or the like which has an upperswivel body and a lower travel body and which runs with an hydraulicallydriven motor provided with an auxiliary speed change gear capable ofchanging between high and low speed ranges, the auxiliary speed changegear is of constant-mesh type and is manually operated by means of anoperation lever to change speeds between high and low speeds. Speedchange operation therefore requires that the vehicle be stoppedtemporarily, and is thus troublesome: it is difficult to conduct speedchange operation quickly and smoothly.

An auxiliary speed change gear which employs a wet multiple disk clutchhydraulically operated to change between high and low speed ranges bymeans of an operation valve has also been proposed in, for example,Japanese Utility Model Laid-Open No. 172817/1986. With this auxiliaryspeed change gear, an operation of shifting a speed changing gear fromlow to high speed, which is conducted while the vehicle is running at ahigh speed, may cause overrun of the hydraulically driven motor anddamage the hydraulic motor or a low speed clutch.

SUMMARY OF THE INVENTION

In view of the aforementioned drawbacks of the prior techniques, anobject of the present invention is to provide an automatic transmissionfor a hydraulically driven auxiliary speed change gear which assureseasy speed changing gear shifting operation during travel and whicheliminates damage to an hydraulically driven motor or the like.

To this end, the present invention provides an automatic transmissionfor a hydraulically driven auxiliary speed change gear which is a powertransmitting speed change gear including a hydraulically driven motorand an auxiliary speed change gear provided with hydraulically operatedclutches to shift between high and low speed ranges. In this automatictransmission, an automatic change-over valve is provided in a hydrauliccircuit which connects cylinders of the high and low speed clutches to aclutch operating hydraulic pump. One end of the automatic change-overvalve is connected to the hydraulic circuit connected to the dischargeside of the pump by a conduit pipe, and an automatic speed changingvalve is provided in the conduit pipe. A rotation sensing hydraulic pumpcoupled to an input shaft of the auxiliary speed change gear isconnected to one end of the automatic speed changing valve and to theother end of the automatic speed changing valve through an orifice. Theother end of the automatic speed changing valve is connected to ahydraulic circuit which is located between the low-speed clutch and theautomatic change-over valve by a conduit pipe. The rotation sensinghydraulic pump may be connected not to the input shaft of the auxiliaryspeed change gear but to an output shaft thereof. Alternatively, theinput shaft of the auxiliary speed change gear may be connected to anannular centrifugal hydraulic pressure detecting chamber which isemployed in place of the rotation sensing hydraulic pump and theorifice. In that case, a pressure detecting pipe inserted in thischamber is connected to one end of the automatic speed change valve.

In a case where the combination of the orifice and the rotation sensinghydraulic pump coupled to an input or output shaft of the auxiliaryspeed change gear is employed, the automatic speed changing valve iscontrolled by utilizing a difference in the discharge pressure of therotation sensing hydraulic pump which varies in accordance with therotation speed of the hydraulically driven motor and the dischargepressure which has passed through the orifice, to change over theautomatic change-over valve due to the pilot pressure from the automaticspeed changing valve and thereby change-over the clutches automaticallywithout damaging the hydraulically driven motor or the like. In the caseof the annular centrifugal hydraulic pressure detecting chamber coupledto the input shaft of the auxiliary speed change gear also, theautomatic speed changing valve is controlled by utilizing thecentrifugal hydraulic pressure which varies in accordance with a changein the rotational speed of the hydraulically driven motor to change overthe automatic change-over valve due to the pilot pressure from theautomatic speed changing valve, as in the above-described case. Inconsequence, this configuration is as advantageous as the case of thecombination of the rotation sensing hydraulic pump and the orifice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an hydraulic circuit of a first embodiment of the presentinvention;

FIG. 2 is a cross-sectional view of an automatic speed changing valveaccording to the present invention;

FIG. 3 is an hydraulic circuit of a second embodiment of the presentinvention;

FIG. 4 is an hydraulic circuit of a third embodiment of the presentinvention;

FIG. 5 shows a centrifugal hydraulic pressure detecting chamberaccording to the present invention; and

FIGS. 6 and 7 show the configurations of planetary gear type auxiliaryspeed change gears.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a hydraulic circuit diagram of a first embodiment of thepresent invention. A gear type auxiliary speed change gear 1, which iscapable of shifting between high and low speed ranges, has anhydraulically operated high-speed clutch 1a and a hydraulically operatedlow-speed clutch 1b. One end of an input shaft 2b of the auxiliary speedchange gear 1 is connected to an hydraulically driven motor 2 providedin an hydraulic circuit which extends from a main pump driven by anengine M mounted on an upper swivel body to a lower travel body via aswivel joint, and the other end of the input shaft 2b driven by themotor 2 is coupled to a rotation sensing hydraulic pump 3. In ahydraulic circuit 30 which extends from the rotation sensing hydraulicpump 3 to a lubricating portion 1R of the auxiliary speed change gear 1is provided an orifice 7. In the hydraulic circuit which extends fromthe upper swivel body to the lower travel body via the swivel joint inthe manner stated above is also provided a clutch operating hydraulicpump driving motor 4, and in a hydraulic circuit 50 which extends from aclutch operating hydraulic pump 5 driven by the driving motor 4 to thecylinders of the high-speed and low-speed clutches 1a and 1b is providedan automatic change-over valve 6. In a conduit pipe 50d which divergesfrom the hydraulic circuit 50 at a point located in advance of theautomatic change-over valve 6 and which reaches one end of the automaticchange-over valve 6 is provided an automatic speed changing valve 8.Left end of the automatic speed changing valve 8 is connected to aconduit pipe 30a which diverges from the hydraulic circuit 30 at a pointlocated in advance of the orifice 7, and the right end thereof isconnected to a conduit pipe 30b which diverges from the hydrauliccircuit 30 at a point located behind the orifice 7 and to a conduit pipe50c which diverges from the hydraulic circuit 50 at a point located inadvance of the low-speed clutch 1b.

As shown in detail in FIG. 2, in the automatic speed changing valve 8, aspool 8a and a piston 8b are inserted in a valve body, and a spring 8cis provided between the spool 8a and the piston 8b. The hydrauliccircuit 30 which extends from the rotation sensing hydraulic pump 3 isconnected to the left end of the spool 8a. The hydraulic circuit 30diverges and is also connected to the right end (the portion of thevalve where the spring 8c is inserted) of the spool 8a via the orifice7. The conduit pipe 50b branches into a conduit pipe 50c at a pointbetween the automatic change-over valve 6 and the low-speed clutch 1b,and the conduit pipe 50c is connected to the right end of the piston 8b.The hydraulic circuit 50 branches into the conduit pipe 50d at a pointlocated in advance of the automatic change-over valve 6, and the conduitpipe 50d is connected to one end of the automatic change-over valve 6via a pressurized oil port 8d of the automatic speed changing valve 8.

In the thus-arranged automatic transmission, when the main pump isdriven by the engine M mounted on the upper swivel body, thehydraulically driven motor 2 provided in the hydraulic circuit extendingfrom the main pump to the lower travel body via the swivel joint isdriven. In a case where the vehicle runs in a low speed range which isachieved by the engagement of the low-speed clutch 1b of the auxiliaryspeed change gear 1 , when the rotational speed of the hydraulicallydriven motor 2 is increased to 2700 rpm or above, the high-speed clutch1a is engaged and the speed changing gear is shifted to the high-speedrange. In a case where the vehicle travels in a high-speed range whichis achieved by the engagement of the high-speed clutch 1a, when therotational speed of the hydraulically driven motor 2 is reduced to 800rpm or below, the low-speed clutch 1b is engaged and the speed changegear is shifted to the low-speed range. The inner diameter of theorifice 7 provided in the hydraulic circuit 30 which reaches from therotation sensing hydraulic pump 3, the pressure receiving area of thespool 8a and that of the piston 8b of the automatic speed changing valve8 connected to the hydraulic circuit 30, and the tension of the spring 8are set beforehand to values which assure the above-described speedchange gear shifting operations.

More concretely, the discharge v of the rotation sensing hydraulic pump3 is 10 cc/rev, the diameter d0 of the orifice 7 is 2.7 mm, the diameterd2 of the spool 8a is 15 mm, the diameter d1 of the piston 8b is 28 mm,the tension F3 of the spring 8c is 7 kg, and the hydraulic pressure pfor the high-speed and low-speed clutches is 20 kg/cm². When therotational speed of the hydraulically driven motor 2 is increased to2700 rpm or above while the vehicle is running in the low-speed range,force F2 which presses the spool 8a rightward becomes larger than thesum of force F1 which presses the piston 8b leftward and the tension F3of the spring 8c due to the difference in the pressure in the portion inthe hydraulic circuit 30 located in advance of the orifice 7 and in theportion located behind the orifice 7, moving the spool 8a rightward andthereby closing the port 8d. Since the port 8d is connected to the leftend of the automatic change-over valve 6 via the conduit pipe 50d,closing of the port 8d moves the automatic change-over valve 6 leftward,thereby disengaging the low-speed clutch 1b and engaging the high-speedclutch 1a to attain the high-speed range. When the rotational speed ofthe hydraulically driven motor 2 is decreased to 800 rpm or below whilethe vehicle is running in the high-speed range, although the force F1which presses the spool 8a leftward is zero, the force F2 which pressesthe spool 8a rightward becomes smaller than the tension F3 of the spring8c, moving the spool 8a leftward and thereby opening the port 8d. As aresult, the automatic change-over valve 6 moves rightward which is theopposite direction in which the valve 6 is moved in the above-describedcase, and the high-speed clutch 1a is disengaged and the low-speedclutch 1b is engaged to attain the low-speed range.

In FIG. 1, when a shift valve 20 provided in the upper swivel body ispositioned at neutral N, a neutral valve 21 provided in the lower travelbody is moved to the neutral position N due to the air pilot pressure,making the hydraulic circuit 50 neutral. A modulation valve 22 and aquick returning valve 23 have the function of lowering the degree atwhich the hydraulic pressure for the clutch is increased to shift thespeed change gear and of reducing the impacts imparted when the speedrange is changed over.

In this embodiment, since the speed change gear is shifted from thehigh-speed range to the low-speed range when the rotational speed of thehydraulically driven motor 2 is reduced to 800 rpm or below, thehydraulically driven motor 2 or the low-speed clutch 1b is not damaged.Furthermore, since the clutch operating hydraulic pump 5 is provided inthe lower travel body and is driven by the dedicated driving motor 4,suction resistance is small and the possibility of the clutch operatinghydraulic pump 5 being damaged is very small as compared with the casein which the clutch operating hydraulic pump is provided in the upperswivel body and is directly driven by the engine M.

FIG. 3 is an hydraulic circuit of a second embodiment of the presentinvention. In FIG. 3, the rotation sensing hydraulic pump 3 is coupledto an output shaft 2a of the auxiliary speed change gear 1. Otherstructures and advantages are the same as those of the first embodiment.

FIG. 4 is an hydraulic circuit of a third embodiment of the presentinvention. In this embodiment, a centrifugal hydraulic pressuredetecting chamber 9 is provided in place of the combination of therotation sensing hydraulic pump 3 and the orifice 7 which are employedin the first embodiment. FIG. 5 shows this centrifugal hydraulicpressure detecting chamber 9. In the annular centrifugal hydraulicpressure detecting chamber 9 which is coupled to the input shaft 2b ofthe auxiliary speed change gear 1 is charged, an hydraulic oil of thesame type which is charged in other circuits. A pressure detecting pipe10 is inserted into the centrifugal hydraulic pressure detecting chamber9. This pressure detecting pipe 10 is connected to one end of theautomatic speed changing valve 8 via an hydraulic circuit 90 to transmita centrifugal hydraulic pressure P in the centrifugal hydraulic pressurechamber 9, which varies in accordance with a change in the rotationalspeed of the input shaft 2b, to the automatic speed changing valve 8 asa shift pressure. Other structures and advantages are the same as thoseof the first embodiment.

The gear mechanism of the auxiliary speed change gear may also compriseeither of epicyclic gear mechanisms shown in FIGS. 6 and 7. In theauxiliary speed change gear shown in FIG. 6, power transmitted to a sungear 1c from the hydraulically driven motor 2 through the input shaft 2bis transmitted to a plurality of planetary gears 1d provided on theouter periphery of the sun gear 1c. On the outer periphery of theplanetary gears 1d is provided a ring gear 1e. In a case where thevehicle travels in the low-speed range, since the low-speed clutch 1j isengaged, the ring gear 1e is fixed and the planetary gears 1d rotatewithin the ring gear 1e and thereby transmit a reduced rotation to aplanetary carrier 1f. The power of the planetary carrier 1f istransmitted to the output shaft 2a through a drive gear 1g fixed to theshaft of the planetary carrier 1f and a driven gear 1h engaged with thedrive gear 1g. In a case where the vehicle runs in the high-speed range,the high-speed clutch 1k is engaged, and the sun gear 1c is therebyrotated together with the ring gear 1e. As a result, the rotation of theinput shaft 2b is transmitted without being reduced to the planetarycarrier 1f.

In the auxiliary speed change gear shown in FIG. 7, when the high-speedclutch 1k is engaged, the sun gear 1c and the planetary carrier 1f arerotated as one unit. As a result, the rotation of the input shaft 2b istransmitted to the planetary carrier 1f efficiently. In the case of thetravelling in a low-speed range, the structure and the advantage are thesame as those shown in FIG. 6.

INDUSTRIAL APPLICABILITY

As will be understood from the foregoing description, the automatictransmission according to the present invention is useful as anautomatic transmission for a hydraulic excavator which has an auxiliaryspeed change gear capable of automatically change over speeds betweenthe high and low speed ranges without damaging the hydraulically drivenmotor or the like.

What is claimed is:
 1. An automatic transmission for a hydraulicallydriven auxiliary speed change gear which is a power transmitting/speedchange gear including a hydraulically driven motor and an auxiliaryspeed change gear provided with hydraulically operated clutches engagedand disengaged to attain high and low speeds, said automatictransmission comprising:an automatic change-over valve provided in ahydraulic circuit which connects said high and low speed clutches to aclutch operating hydraulic pump, a first conduit pipe which conducts oneend of said automatic change-over valve to a hydraulic circuit connectedto a discharge side of said clutch operating hydraulic pump, anautomatic speed changing valve provided in said first conduit pipe, arotation sensing hydraulic pump coupled to an input shaft of saidauxiliary speed change gear, a second conduit pipe which connects ahydraulic circuit connected to a discharge side of said rotation sensinghydraulic pump to one end of said automatic speed changing valve, athird conduit pipe which connects the hydraulic circuit connected to thedischarge side of said rotation sensing hydraulic pump to the other endof said automatic speed changing valve through an orifice, and a fourthconduit pipe which connects the other end of said automatic speedchanging valve to a hydraulic circuit which is located between saidlow-speed clutch and said automatic change-over valve.
 2. An automatictransmission comprising:an auxiliary speed change gear which is a powertransmitting/speed change gear, said auxiliary speed change gear havingan input shaft and an output shaft, a hydraulically operated high speedclutch engagable between said input shaft and said output shaft toattain a high speed range, a hydraulically operated low speed clutchengagable between said input shaft and said output shaft to attain a lowspeed range, said auxiliary speed change gear being capable of shiftingbetween said high and low speed ranges; a hydraulically driven motor fordriving said input shaft; a clutch operating hydraulic pump having adischarge side, an automatic change-over valve, a first hydrauliccircuit which connects said high speed clutch to said automaticchange-over valve, a second hydraulic circuit which connects said lowspeed clutch to said automatic change-over valve, a third hydrauliccircuit which connects said automatic change-over valve to the dischargeside of said clutch operating hydraulic pump, said automatic change-overvalve selectively connecting said third hydraulic circuit to one of saidfirst and second hydraulic circuits; a fourth hydraulic circuit whichconnects a pilot port of said automatic change-over valve to saiddischarge side of said clutch operating hydraulic pump, an automaticspeed changing valve provided in said fourth hydraulic circuit betweensaid discharge side of said clutch operating hydraulic pump and saidpilot port of said automatic change-over valve, said automatic speedchanging valve having first and second pilot ports such that thepressures therein are in opposition to each other; a rotation sensinghydraulic source coupled to one of said input shaft and said outputshaft, said rotation sensing hydraulic source having a discharge side; afifth hydraulic circuit which connects the discharge side of saidrotation sensing hydraulic source to the first pilot port of saidautomatic speed changing valve; and a sixth hydraulic circuit whichconnects the second pilot port of said automatic speed changing valve tosaid second hydraulic circuit.
 3. An automatic transmission inaccordance with claim 2 wherein said automatic speed changing valve hasa third pilot port wherein the pressure is in opposition to the pressurein said first pilot port; wherein said rotation sensing hydraulic sourcecomprises a rotation sensing hydraulic pump; and wherein said automatictransmission further comprises an orifice, and a seventh hydrauliccircuit which connects the discharge side of said rotation sensinghydraulic pump through said orifice to the third pilot port of saidautomatic speed changing valve.
 4. An automatic transmission inaccordance with claim 3 wherein said rotation sensing hydraulic pump iscoupled to said input shaft.
 5. An automatic transmission in accordancewith claim 3 wherein said rotation sensing hydraulic pump is coupled tosaid output shaft.
 6. An automatic transmission in accordance with claim3 wherein said automatic speed changing valve comprises a valve bodyhaving first, second, third and fourth cavities therein, a spoolpositioned in said valve body and extending from its first end in saidfirst cavity through said second cavity to its second end in said thirdcavity, a piston positioned in said fourth cavity and having a axialportion extending into said third cavity for selective engagement withthe second end of said spool, and a spring positioned to bias said spooltoward said first cavity, said fourth hydraulic circuit including saidsecond cavity, said first pilot port being connected to said firstcavity, said second pilot port being connected to said fourth cavitysuch that pressure in said sixth hydraulic circuit urges said pistontowards said spool, and said third pilot port being connected to saidthird cavity.
 7. An automatic transmission in accordance with claim 2wherein said rotation sensing hydraulic source comprises an annularcentrifugal hydraulic pressure detecting chamber having a pressuredetecting pipe positioned therein.
 8. An automatic transmission inaccordance with claim 7 wherein said rotation sensing hydraulic sourceis coupled to said input shaft.
 9. An automatic transmission inaccordance with claim 7 wherein said rotation sensing hydraulic sourceis coupled to said output shaft.
 10. An automatic transmission inaccordance with claim 7 wherein said automatic speed changing valvecomprises a valve body having first, second, third and fourth cavitiestherein, a spool positioned in said valve body and extending from itsfirst end in said first cavity through said second cavity to its secondend in said third cavity, a piston positioned in said fourth cavity andhaving a axial portion extending into said third cavity for selectiveengagement with the second end of said spool, and a spring positioned tobias said spool toward said first cavity, said fourth hydraulic circuitincluding said second cavity, said first pilot port being connected tosaid first cavity, and said second pilot port being connected to saidfourth cavity such that pressure in said sixth hydraulic circuit urgessaid piston towards said spool.
 11. An automatic transmission inaccordance with claim 2 further comprising a shift valve and a neutralvalve, said neutral valve being in said third hydraulic circuit, andsaid neutral valve being selectively positioned to pass fluid from saidclutch operating hydraulic pump to one of said automatic change-overvalve and a lubrication portion of said auxiliary speed change gear inaccordance with the position of said shift valve.
 12. An automatictransmission in accordance with claim 2 wherein said automatic speedchanging valve comprises a valve body having first, second, third andfourth cavities therein, a spool positioned in said valve body andextending from its first end in said first cavity through said secondcavity to its second end in said third cavity, a piston positioned insaid fourth cavity and having a axial portion extending into said thirdcavity for selective engagement with the second end of said spool, and aspring positioned to bias said spool toward said first cavity, saidfourth hydraulic circuit including said second cavity, said first pilotport being connected to said first cavity, and said second pilot portbeing connected to said fourth cavity such that pressure in said sixthhydraulic circuit urges said piston towards said spool.
 13. Ahydraulically driven vehicle comprising:an upper swivel body and a lowertravel body having a swivel joint therebetween; an automatictransmission positioned on said lower travel body, said automatictransmission comprising: an auxiliary speed change gear which is a powertransmitting/speed change gear, said auxiliary speed change gear havingan input shaft and an output shaft, a hydraulically operated high speedclutch engagable between said input shaft and said output shaft toattain a high speed range, a hydraulically operated low speed clutchengagable between said input shaft and said output shaft to attain a lowspeed range, said auxiliary speed change gear being capable of shiftingbetween said high and low speed ranges; a hydraulically driven motor fordriving said input shaft; a clutch operating hydraulic pump having adischarge side, an automatic change-over valve, a first hydrauliccircuit which connects said high speed clutch to said automaticchange-over valve, a second hydraulic circuit which connects said lowspeed clutch to said automatic change-over valve, a third hydrauliccircuit which connects said automatic change-over valve to the dischargeside of said clutch operating hydraulic pump, said automatic change-overvalve selectively connecting said third hydraulic circuit to one of saidfirst and second hydraulic circuits; a fourth hydraulic circuit whichconnects a pilot port of said automatic change-over valve to saiddischarge side of said clutch operating hydraulic pump, an automaticspeed changing valve provided in said fourth hydraulic circuit betweensaid discharge side of said clutch operating hydraulic pump and saidpilot port of said automatic change-over valve, said automatic speedchanging valve having first and second pilot ports such that thepressures therein are in opposition to each other; a rotation sensinghydraulic source coupled to one of said input shaft and said outputshaft, said rotation sensing hydraulic source having a discharge side; afifth hydraulic circuit which connects the discharge side of saidrotation sensing hydraulic source to the first pilot port of saidautomatic speed changing valve; and a sixth hydraulic circuit whichconnects the second pilot port of said automatic speed changing valve tosaid second hydraulic circuit; an engine and a main hydraulic pumplocated on said upper swivel body, said main hydraulic pump being drivenby said engine; a seventh hydraulic circuit connecting saidhydraulically driven motor to the output of said main hydraulic pump, asecond hydraulically driven motor positioned on said lower travel bodyto drive said clutch operating hydraulic pump; and an eighth hydrauliccircuit connecting said second hydraulically driven motor to the outputof said main hydraulic pump.
 14. A hydraulically driven vehicle inaccordance with claim 13 further comprising a shift valve positioned onsaid upper swivel body, and a neutral valve positioned in said thirdhydraulic circuit, said neutral valve being selectively positioned topass fluid from said clutch operating hydraulic pump to one of saidautomatic change-over valve and a lubrication portion of said auxiliaryspeed change gear in accordance with the position of said shift valve.15. A hydraulically driven vehicle in accordance with claim 13 whereinsaid automatic speed changing valve has a third pilot port wherein thepressure is in opposition to the pressure in said first pilot port;wherein said rotation sensing hydraulic source comprises a rotationsensing hydraulic pump; and wherein said automatic transmission furthercomprises an orifice, and a ninth hydraulic circuit which connects thedischarge side of said rotation sensing hydraulic pump through saidorifice to the third pilot port of said automatic speed changing valve.16. A hydraulically driven vehicle in accordance with claim 15 furthercomprising a shift valve positioned on said upper swivel body, a neutralvalve positioned in said third hydraulic circuit, said neutral valvebeing selectively positioned to pass fluid from said clutch operatinghydraulic pump to one of said automatic change-over valve and alubrication portion of said auxiliary speed change gear in accordancewith the position of said shift valve.
 17. A hydraulically drivenvehicle in accordance with claim 13 wherein said rotation sensinghydraulic source comprises an annular centrifugal hydraulic pressuredetecting chamber having a pressure detecting pipe positioned therein.18. A hydraulically driven vehicle in accordance with claim 17 furthercomprising a shift valve positioned on said upper swivel body, a neutralvalve positioned in said third hydraulic circuit, said neutral valvebeing selectively positioned to pass fluid from said clutch operatinghydraulic pump to one of said automatic change-over valve and alubrication portion of said auxiliary speed change gear in accordancewith the position of said shift valve.